When a well is drilled, production casing is set so that the well is properly cemented and the production zones do not have communication. The production zone is logged and then perforated so that flow of oil or gas can be drained from the oil or gas bearing zone into a production casing of the well. Traditionally, hydrocarbon wells were drilled vertically down to and through one or more production zone(s). Over the last decade horizontal drilling techniques have evolved. Wells are now drilled vertically to a point just above the production zone and then curved so that the well bore enters the production zone at an angle and continues laterally within the production zone for more in-zone exposure to the formation. Some production zones are up to 300 feet (91.5 meters) thick and with horizontal drilling techniques casing can be run up to 10.000 ft. (3 kilometers) into the production zone, thus providing significantly more drainage area into the production casing. Horizontal drilling also enables the drilling of multiple horizontal bores in different directions from a pad of 2 or more wells. This speeds up drilling and uses less footprint to drain the production zone(s). It also permits drilling under lakes, cities and property that would create hardship for land owners if drilling had to be performed in the traditional manner.
FIG. 1 is a schematic cross-sectional diagram of an exemplary prior art long lateral well bore 10. Well know features such as the conductor and surface casing are not shown. A vertical section 12 of the well bore 10 is drilled vertically into proximity of a production zone 14, cased and cemented in a manner well known in the art. In many areas, the vertical section of the well may be up to 10,000 feet (3 kilometers) in length. A curved section 16 of the well bore is then drilled into the production zone 14. Once it is established that the curved section is in the production zone 14, a lateral bore 18 is drilled in a desired direction in as straight a path as possible within the production zone. As is well understood in the art, the horizontal bore 18 is generally somewhat corkscrew shaped due to remote control of the drill motor. If the lateral bore is very long, a first section having a length of HL1 (5,000 feet or more, for example) may be drilled for 5.5″ casing and a second section 22 having a length of HL2 (3,000-5,000 feet or more) may be drilled for 4.5″ casing. However, this is exemplary only and not required. The curved section and the lateral bore are then cased and cemented. If the horizontal bore requires two different casing sizes, a casing transition sub 20 is used to connect the 5.5″ casing to the 4.5″ casing.
Conventional tubing has been successfully used for years as a work string for completing vertical and horizontal bores. Those skilled in the art understand that work strings are used to perform many completion functions including setting packers or plugs 24 at predetermined intervals for the purpose of fracture treating the production zone 14. Chemical treatments 26, such as acids or other production aids may also be injected into the well using a tubing work string. As described above, when well bores with long laterals are drilled there is generally considerable deviation in the lateral bore due to remote steering of the drill motor. Since the work string has to wind through those deviations for completion purposes, more torque is required to turn the string to perform many desired completion functions. As a result, attempts to complete lateral bores that exceed 5,000 feet (1.5 kilometers) using tubing work strings is fraught with problems because the tubing buckles or shears. Such problems cause delays and increase well completion expense.
There therefore exists a need for a novel work string and a method of completing long lateral well bores.